Dynamic elaboration on the Art & Science of Hazardous Area Protection
Selection of a proper, Hazardous Area Complied Cable Gland is an important factor. The normal working and safety of the Junction/Terminal boxes, control stations and all electrical devices comprising the electrical network in the Hazardous Area depend, among other factors upon the installed Cable Gland.
Hazardous Area Experience and proper respective trainings are, of course the prerequisites for the concerned design engineer.
IEC 60079-14 -Edition 5 gives a table for the selection of Glands according to protection techniques , as given in different sections of the same standard.
(Reference : IEC 60079-14 Edition 5)
Salient features of the Sections 10.6, 10.4 & 10.7
Section 10.6 : Additional Requirements for Flameproof Enclosures : Ex d
Some of the important point are listed as follow:
1. In case the electrical connection to the flameproof enclosure is through BUSHINGS , then the parts of the bushing outside the Flameproof enclosure should be protected by proper means as in IEC 60079-0, by enclosing them in another flameproof enclosure or Increased-safety enclosure.
The bushings are permitted to be used as current feeders in enclosures with type of protection ”flameproof”. They are fitted into the enclosure wall and provide an insulated current path across the Flame-Proof Enclosure wall.
Typical Construction consists of a Duct bolt , located in the middle of a ring nut and the parts are bonded with a high-quality, track resistant insulating material (epoxy resin) to form an inseparable unit.
2. If an Ex d Gland is being used with BRAIDED or ARMOURED cables then compression should be proper. Flame propagation may occur through the very small spaces (interstices) which may exist between the strands of a stranded conductor or through the space between the individual cores of a multi-core cable. This can be prevented by the use of special cable construction. ( Restricted Breathing test for cables may be carried out to check for the hidden spaces within the cable which can help in FLAME Propagation through the cable length)
3. Sealing washers may be used with Cable Glands , adapters or plugs having parallel threads during installation into the Flameproof enclosure provided that FIVE FULL THREADS Engagement is still possible .
4. Any alteration to the thread type or addition of holes is only permitted when this process is :-
For more details , see IEC 60079-14 -Edition 5
Some of the points are as follows:
Additional cable-entry holes are permitted for other than Ex d, Ex t or Ex nR , as per Manufacturer’s documents regarding the size, quantity and tolerances.
(Protection By Enclosure :Type Ex t . The guidelines are given in IEC 60079-31)
In IEC 60079-14 additional requirements (guidelines) are given as to the IP Rating and corresponding Ex t protection as per following Table:-
|Level of Protection||GROUP IIIC||GROUP IIIB||GROUP IIIA|
Sealing washers may be used with Cable Glands , adapters or plugs having parallel threads during installation into the “t” enclosure provided that FIVE FULL THREADS Engagement is still possible .
Tapered threaded joints without an addition seal or gasket the minimum thread engagement is 3½.